This invention generally relates to slider-operated zippers for use in reclosable packaging, such as bags or pouches. In particular, the invention relates to sliders of the type that do not have a separating finger.
Reclosable bags are finding ever-growing acceptance as primary packaging, particularly as packaging for foodstuffs such as cereal, fresh vegetables, snacks and the like. Such bags provide the consumer with the ability to readily store, in a closed, if not sealed, package any unused portion of the packaged product even after the package is initially opened. To gain acceptance as a primary package for foodstuffs, it is virtually mandatory that the package exhibit some form of tamper evidence to protect the consumer and maintain the wholesomeness of the contained product. In addition, in many cases it is necessary that food product be hermetically packaged.
Reclosable fastener assemblies are useful for sealing thermoplastic pouches or bags. Such fastener assemblies typically include a plastic zipper and a plastic slider. Typically, the plastic zippers include a pair of interlockable profiled members that form a closure. As the slider moves across the profiles, the profiles are opened or closed. The profiles in plastic zippers can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure members, etc. Reclosable bags having slider-operated zippers are generally more desirable to consumers than bags having zippers without sliders because the slider eliminates the need for the consumer to align the interlockable zipper profiles before causing those profiles to engage.
In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction. Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled closure members, portions of which form a fulcrum about which the profiled closure members may be pivoted out of engagement when lower edges of the bases are forced towards each other.
Another known slider of the above-described type has a so-called “keeper” projecting vertically downward from the opening end of the top wall of the slider. The keeper mates with a recess in the male-profiled closure member of the zipper, holding the male-profiled closure member partially away from the female-profiled closure member. By preventing movement of the one closure member towards the other closure member, the zipper profiles always remain at least partially disengaged at the opening end of the slider, thereby reducing the possibility of an unintentional full engagement of the closure members adjacent the opening end or within the slider and facilitating the opening movement of the zipper. In one known slider insertion machine, the zipper tape is “activated” during slider insertion The term “activation” as used herein means that opposing sections of the zipper closure members at the opening end of the slider are at least partially disengaged and held in that state by the keeper. The term “deactivation” as used herein means that the zipper profiles become engaged at the opening end of the slider and are no longer held partly disengaged by the keeper.
The above-described slider-operated zipper, with keeper maintaining the zipper in an activated state, must perform satisfactorily over a wide range of temperatures. In particular, it is desirable that this slider/zipper system perform satisfactorily under freezer temperature conditions, to wit, −5° F. to +5° F. The zipper becomes very stiff at these temperatures. This leads to much higher forces to move the slider back and forth along the zipper. The increased zipper stiffness can also lead to deactivation of the slider/zipper assembly since the recess will not stay on the keeper, which renders the reclosable zipper very difficult to operate, if not non-functional. There is a need for a slider design that reduces the tendency of the slider-zipper assembly to deactivate under freezer conditions.